$25 blood test identifies any virus you've ever had

A newly-developed $25 (£16) test that can identify any virus that has ever affected a person, from one drop of blood. It's inventors say it can test for more than 1,000 virus strains, and once refined would be cheap enough to deploy on a large scale. "VirScan is a little like looking back in time: using this method, we can take a tiny drop of blood and determine what viruses a person has been infected with over the course of many years," said co-author on a paper announcing the news in Science, Stephen Elledge of Harvard Medical School. "What makes this so unique is the scale: right now, a physician needs to guess what virus might be at play and individually test for it. With VirScan, we can look for virtually all viruses, even rare ones, with a single test."

The team (which includes researchers from Brigham and Women's Hospital) points out that standard blood tests use biochemistry assays to seek out specific antigens in the blood, a unique marker linked with a specific viral infection. They have to do this separately, for each virus a doctor thinks might be present at that specific time. In contrast, VirScan can simultaneously screen for antibodies related to 206 species of virus that affect humans, and 1,000 strains. This is how it can detect both old and new viruses in the blood -- antibodies produced by the body's immune system to combat a virus remain in the blood stream for many years.

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So far VirScan has delivered accurate results, with almost 100 percent sensitivity for HIV and Hepatitis C in a small trial of people known to have those viruses. "We didn't falsely identify people who were negative," said Elledge. "That gave us confidence that we could detect other viruses, and when we did see them we would know they were real."

The test does have its shortcomings, however. Although it performed very well in the HIV and Hepatitis C studies, when tested against a wider pool of nearly 600 blood samples Chicken Pox was identified in only 25-30 percent of people. "That's much lower than you'd expect," Tomasz Kula, a graduate student working in Elledge's lab, told WIRED.co.uk. "Often times people are vaccinated for it or had it when they were very young, and it wanes over time. So we know we're not the best when it comes to this."

Devising the test over the past two and a half years was no easy feat, and was only made possible thanks to advances in genetic sequencing. Virus proteins were collected from 93,000 short pieces of DNA already sequenced by other scientists. The results represented more than 1,000 virus strains. The team then set about creating a kind of artificial vehicle, or "library", that would contain an element of every single one of those viruses to be tested against, in the form of a bacteriophage -- a virus that attacks bacteria.

VirScan works by exposing a drop of blood onto a bacteriophage populated with peptides, the protein targets antibodies in the immune system attack and hook onto. If there is an antibody in that blood sample related to one of the 1,000 virus strains coded into the bacteriophage, it will seek it out and bind to the related protein. The test then collects up all the antibodies and the matter they have bound to. That matter -- made up of the proteins the antibodies have clung to -- are then sequenced to identify the viruses.

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VirScan, says Elledge, could process 100 samples in around two to three days, and that speed will only increase as the process is fine-tuned.

It has already been tested on blood samples from 569 people from the US, South Africa, Thailand and Peru. The idea was to get as broad a sample range as possible, so the team could also learn more about how immunity works in different geographical areas. It turns out that people have an average of ten different virus species in their bloodstream, with fewer among children, and two individuals testing for up to 84 species.

Although the test is not yet ready to be commercialised, the team hopes it can continue to be used in research now. "We think we can use this to look at correlations between more complex diseases," Kula tells WIRED.co.uk. He suggests that MS or chronic fatigue could be investigated further using VirScan -- both disorders might have underlying viral triggers not yet identified. We want to look at a population of patients with a particular disease and pick out past and ongoing exposures." "Furthermore, right now people are only tested for a virus if there is a reason to suspect it. But many people are walking around with infections like Hep C and don't know about it because they haven't been tested. Because this is very affordable, it can become a standard test where people are checked for viral exposures regularly."